Not applicable.
Not applicable.
The invention relates to a heating device, particularly an engine-independent vehicle heater, with a connecting pipe that communicates with a combustion chamber and is connected to a fuel supply means, with a glow plug which is fastened in the connecting pipe and serves to vaporize and ignite the fuel, at least during a starting phase of the heater, and with a sieve element which is arranged in the connecting pipe, surrounds the glow plug, and passes-on the fuel supplied to the connecting pipe toward the combustion chamber. In conventional heating devices, the sieve element is fitted into the connecting pipe such that an inner wall of the connecting pipe is covered and lined by the sieve element.
Such a heating device is operated with a fuel, e.g., diesel oil, which is liquid under the surrounding conditions. The glow member, e.g., a glow plug or a glow pin, is activated during a starting phase in order to produce heat to ignite the heating device. As soon as the glow member has reached a sufficient temperature in a glow zone, the fuel and fresh air are fed to the connecting pipe according to a special starting procedure. The liquid fuel then enters the connecting pipe and flows along an inner wall of the pipe connection, where the liquid fuel comes into contact with the sieve element lining the inner wall of the connecting pipe. The liquid fuel is sucked up and transported along the inner wall of the connecting pipe toward the combustion chamber, because of a capillary effect due to the structure of the sieve element, which is usually formed by a wire fabric. Since the sieve element envelops the glow member, the liquid fuel distributed on the large surface of the sieve element is evaporated by the heating effect of the glow member. As soon as an ignitable mixture has formed, the combustion of the air-fuel mixture automatically takes place. The combustion chamber can then be ignited by the combustion attained in the connecting pipe. As soon as a stable combustion is present in the combustion chamber, the glow member can be deactivated again.
The glow member must meet high performance requirements in order to ensure a reliable ignition of the fuel respectively used. For example, a relatively high temperature has to be attained with the glow member, due to which the working and service life of the glow member is reduced. In particular, the use of so-called xe2x80x9cbiodieselxe2x80x9d or xe2x80x9cPMExe2x80x9d as the fuel is achieving increasing importance, but requires a particularly large heat supply for evaporation and ignition.
The present invention is concerned with the problem of designing a heating device of the kind stated at the beginning so that an increased working life of the glow member can be ensured. The heating device is furthermore to be operated with fuels such as biodiesel which boil with relative difficulty. This problem is solved according to the invention by a heating device with the features of a fuel supply, a connecting pipe having an inner wall, which communicates with a combustion chamber and is connected to the fuel supply, a glow member, which is fastened in the connecting pipe and serves to evaporate and ignite fuel, at least during a starting phase of the heating device, a sieve element, which is arranged in the connecting pipe, surrounds the glow member, and passes-on fuel supplied to the connecting pipe in a direction of the combustion chamber. The sieve element is spaced within the connecting pipe from at least a region of the inner wall facing toward the sieve element.
The invention is based on the general concept of arranging the sieve element in the connecting pipe in a manner such that a spacing or gap is formed between the sieve element and the inner wall of the connecting pipe, at least in some regions. The regional spacing of the sieve element from the inner wall can be formed, for example, by an annular gap. It is likewise possible to form several, axially spaced-apart, annular spaces. Several axially-extending spacing-apart spaces can also be formed, distributed along the external circumference of the sieve element. A separating space which extends helically is also conceivable. In this manner the sieve element regionally has no contact with the inner wall of the connecting pipe, so that heat dissipation from the sieve element to the inner wall of the connecting pipe is reduced in these regions. This measure has the result that the sieve element and thus the fuel distributed over the surface of the sieve element requires less energy to attain the desired evaporation of the fuel. Correspondingly, a lower glow temperature is sufficient for the glow member in comparison with conventional heating devices, in order to evaporate and to ignite a usual kind of fuel. Since the glow member can thus be operated at lower glow temperatures, a longer service life of the glow member, and thus overall an increased use value for the heating device, are attained. It has furthermore been found that even fuels which boil with relative difficulty can be reliably ignited, without further measures, in the heating device constructed according to the invention. Correspondingly, the heating device according to the invention can be operated with fuels which boil or ignite with difficulty, such as e.g. biodiesel.
Corresponding to a preferred embodiment, the sieve element can be spaced apart, at least in a region surrounding the glow zone of the glow member, from the inner wall of the connecting pipe. In this region, the separation of the thermal coupling between the sieve element and the connecting pipe inner wall acts particularly clearly, since a particularly large temperature difference exists here in the starting phase between the glow member and the inner wall of the connecting pipe.
The sieve element can appropriately be fastened to the connecting pipe and/or to the glow member in a region remote from the glow zone of the glow member. The glow member has only a small heat development in this region, so that a thermally conducting bridge between the sieve element and the inner wall of the connecting pipe exhibits only a small effect on the evaporation of the fuel.
An embodiment of the invention in which at least one projection portruding from the sieve element toward the connecting pipe inner wall, and by means of which the sieve element is supported on the connecting pipe inner wall, is formed on the sieve element in a fastening region in which the sieve element is fastened or fixed to the connecting pipe.
By means of this feature, on the one hand the connecting pipe has a relatively large internal cross section, so that the transport of relatively large amounts of fuel can be ensured. On the other hand, the sieve element thereby also has a relatively large cross sectional surface, so that the suction effect of the sieve element is particularly large. A large suction effect of the sieve element is desired because a relatively large amount of fuel can thereby be conducted away from the glow member. Fuel which is distributed over the surface of the glow member causes cooling of the glow member on evaporation, thereby reducing its performance.
According to an embodiment of the invention, the sieve element can consist of a wire fabric, which has more layers of fabric in the region of the at least one projection than in the regions adjacent thereto. For example, the wire fabric of the sieve element can be made five-layered in the region of the at least one projection and three-layered in the remaining regions. The sieve element has an increased suction effect in the region of the projection because the wire fabric has more fabric layers in the region of the projection than in the regions adjacent thereto. A sieve element can be produced particularly easily from wire fabric. The wire fabric is preferably made from a steel wire. The sieve element can however be made from other materials as long as the required suction and transport effect is ensured. For example, a porous body is also suitable, and can in particular be made in one piece from a sintered material. Such a sintered body can be made, e.g., from a steel powder.
Further important features and advantages of the apparatus according to the invention will become apparent from the drawings and from the associated description of the Figures with reference to the drawings.
It will be understood that the features mentioned above and those to be explained hereinafter can be used, not only in the given combination, but also in other combinations or alone, without departing from the scope of the invention.